Abstract

A form of apparent visual movement which occurs when spatio-temporally random visual noise is confined in an annular channel has been investigated. The phenomenon, known as the Omega Effeot, does not seem to be related to the phi-phenomenon, although there are formal similarities with observations sometimes made in certain stroboscopically illuminated fields.The period of omega movement was found to be independent of most of the statistics of the visual noise used to evoke it.Over 100 subjects were tested with a variety of stimulus-annuli. Although large individual differences occurred, the mean period and variance of most Ss did not generally vary, although there was some dependence on performance in the recent past. Significant sex differences were found in estimates of the mean period.The more of observation had little effect that could be measured. Simple, circular annuli evoked the clearest and most consistent reports of apparent movement. The two parameters which conditioned the mean period p were found to be the annulus diameter D and the channel thickness T. For large enough groups of' Ss , it was shown that p = K1 D log T + K2 log T + K3 D + K4 fitted the experimental data very closely.It was demonstrated that both changes in distance and changes in angle of regard affected the mean period, there existing a negative and a positive correlation, respectively. The former finding was in agreement with prediction, but the latter was not. It was postulated that the effect depends to at least some extent on the presence of long-range interactions which possibly exceed the limits normally found in the retina. Some suggestions are made for possible future work.